Poorly Brahma pullet

Hi guys,
I bought 2 18 week old brahma pullets 8 weeks ago,both were in good health but the partridge one got picked on by other members of my flock and I thought she wasn't gonna make it but she got segregated for a day or two and built her strength up and now she's as strong as an ox ,twice the size she was when I got her and she's a Stunning young hen,however the stronger of the two,the black brahma,who would protect her from bullying by standing between her and the aggressor has deteriorated somewhat over the past week or so,she's not grown much since getting her compared to her sister,when I pick her up her crop is always empty even though she grazes all day long with the rest of the flock and she's very light.now I'm noticing she's only got her eyes half open,she sits hunched up and walks on hunched up legs,with feathers always fluffed up....I'd just like to know if these symptoms relate to something specific or is she just under the weather and in need of some t.l.c?
Any help as always wold be greatly appreciated.

Sorry to hear about that,I blame 2 poor quality silver laced Wyandotte bantams that I bought from a guy who wasn't keeping his birds in the best conditions,the things have sneezed since I bough them!..they're all on ipecac c30 and apple cider vinegar,hope it helps.

Sounds like Mareks. Mareks is a highly contagious herpes virus that is pretty much in all flocks now. It causes a slow decline in the bird and eventually death. I have had some hens recover but they never thrive and die fairly young. The only solution to the disease is vaccination withing 24 hours of hatching. A new and more virulent form of mareks is now jumping the vaccine, so purchases from large scale breeders or clearing houses of different breeders really needs to be done with care. Separate your hen and keep her quiet, feeding her high protein feed and even some electrolyte water. Brahmas are tough and strong, she may pull through but will not be super strong.

Wow...that sounds really serious!..the other brahma I bought that survived is a big,strong beautiful example ,only the wyandottes appear unwell but even they only have a cough of sorts,otherwise fine and healthy?